Mechanisms for human cytomegalovirus-induced cytoplasmic p53 sequestration in endothelial cells

Integrins in Cardiovascular Health and Disease: Molecular Mechanisms and Therapeutic Opportunities

Cardiovascular diseases, including atherosclerosis, hypertension, and heart failure, remain the leading cause of global mortality, with endothelial dysfunction and vascular remodeling as critical contributors. Integrins, as transmembrane adhesion proteins, are central regulators of cell adhesion, migration, and signaling, playing a pivotal role in maintaining vascular homeostasis and mediating pathological processes such as inflammation, angiogenesis, and extracellular matrix remodeling. This article comprehensively examines the role of integrins in the pathogenesis of cardiovascular diseases, focusing on their dysfunction in endothelial cells and interactions with inflammatory mediators, such as TNF-α. Molecular mechanisms of integrin action are discussed, including their involvement in mechanotransduction, leukocyte adhesion, and signaling pathways that regulate vascular integrity. The review also highlights experimental findings, such as the use of specific integrin-targeting plasmids and immunofluorescence to elucidate integrin functions under inflammatory conditions. Additionally, potential therapeutic strategies are explored, including the development of integrin inhibitors, monoclonal antibodies, and their application in regenerative medicine. These approaches aim not only to mitigate pathological vascular remodeling but also to promote tissue repair and angiogenesis. By bridging insights from molecular studies with their translational potential, this work underscores the promise of integrin-based therapies in advancing the management and treatment of cardiovascular diseases.

Vitamin D3 Suppresses Human Cytomegalovirus-Induced Vascular Endothelial Apoptosis via Rectification of Paradoxical m6A Modification of Mitochondrial Calcium Uniporter mRNA, Which Is Regulated by METTL3 and YTHDF3

Human cytomegalovirus (HCMV) infection can induce apoptosis of vascular endothelial cells, which may be the most important element of development and progression of reported atherosclerosis caused by HCMV. As there are no specific drugs to clear HCMV infection, exploration of relevant drugs and mechanisms that can intervene in HCMV-induced atherosclerosis is urgently needed. The present study confirmed that vitamin D3 protected vascular endothelial cells from HCMV-induced apoptosis by inhibiting endoplasmic reticulum (ER) and mitochondrial apoptosis pathway. Mechanistically, HCMV infection could induce aberrantly elevated m6A modification, especially the increases of methyltransferases-“writers” (METTL3) and m6A binding proteins-“readers” (YTHDF3). METTL3 methylates mitochondrial calcium uniporter (MCU), the main contributor to HCMV-induced apoptosis of vascular endothelial cells, at three m6A residues in the 3′-UTR, which promotes the association of the YTHDF3 with methylated MCU mRNA and subsequently increases the translation and expression of MCU. Further analysis shows that ALKBH5 is the demethylases-“eraser” of MCU mRNA, which can negatively regulate the m6A modification process of MCU. Conversely, vitamin D3 downregulated the METTL3 by inhibiting the activation of AMPK, thereby inhibiting the m6A modification of MCU and cell apoptosis. Our findings extend the understanding of m6A driven machinery in virus-induced vascular endothelium damage and highlight the significance of vitamin D3 in the intervention of HCMV-induced atherosclerosis.

Murine Cytomegalovirus M25 Proteins Sequester the Tumor Suppressor Protein p53 in Nuclear Accumulations

To ensure productive infection, herpesviruses utilize tegument proteins and nonstructural regulatory proteins to counteract cellular defense mechanisms and to reprogram cellular pathways. The M25 proteins of mouse cytomegalovirus (MCMV) belong to the betaherpesvirus UL25 gene family that encodes viral proteins implicated with regulatory functions. Through affinity purification and mass spectrometric analysis, we discovered the tumor suppressor protein p53 as a host factor interacting with the M25 proteins. M25-p53 interaction in infected and transfected cells was confirmed by coimmunoprecipitation. Moreover, the proteins colocalized in nuclear dot-like structures upon both infection and inducible expression of the two M25 isoforms. p53 accumulated in wild-type MCMV-infected cells, while this did not occur upon infection with a mutant lacking the M25 gene. Both M25 proteins were able to mediate the effect, identifying them as the first CMV proteins responsible for p53 accumulation during infection. Interaction with M25 proteins led to substantial prolongation of the half-life of p53. In contrast to the higher abundance of the p53 protein in wild-type MCMV-infected cells, the transcript levels of the prominent p53 target genes Cdkn1a and Mdm2 were diminished compared to cells infected with the ΔM25 mutant, and this was associated with reduced binding of p53 to responsive elements within the respective promoters. Notably, the productivity of the M25 deletion mutant was partially rescued on p53-negative fibroblasts. We propose that the MCMV M25 proteins sequester p53 molecules in the nucleus of infected cells, reducing their availability for activating a subset of p53-regulated genes, thereby dampening the antiviral role of p53.IMPORTANCE Host cells use a number of factors to defend against viral infection. Viruses are, however, in an arms race with their host cells to overcome these defense mechanisms. The tumor suppressor protein p53 is an important sensor of cell stress induced by oncogenic insults or viral infections, which upon activation induces various pathways to ensure the integrity of cells. Viruses have to counteract many functions of p53, but complex DNA viruses such as cytomegaloviruses may also utilize some p53 functions for their own benefit. In this study, we discovered that the M25 proteins of mouse cytomegalovirus interact with p53 and mediate its accumulation during infection. Interaction with the M25 proteins sequesters p53 molecules in nuclear dot-like structures, limiting their availability for activation of a subset of p53-regulated target genes. Understanding the interaction between viral proteins and p53 may allow to develop new therapeutic strategies against cytomegalovirus and other viruses.

The role of human cytomegalovirus in atherosclerosis: a systematic review

Atherosclerosis is a progressive vascular disease with increasing morbidity and mortality year by year in modern society. Human cytomegalovirus (HCMV) infection is closely associated with the development of atherosclerosis. HCMV infection may accelerate graft atherosclerosis and the development of transplant vasculopathy in organ transplantation. However, our current understanding of HCMV-associated atherosclerosis remains limited and is mainly based on clinical observations. The underlying mechanism of the involvement of HCMV infection in atherogenesis remains unclear. Here, we summarized current knowledge regarding the multiple influences of HCMV on a diverse range of infected cells, including vascular endothelial cells, vascular smooth muscle cells, monocytes, macrophages, and T cells. In addition, we described potential HCMV-induced molecular mechanisms, such as oxidative stress, endoplasmic reticulum stress, autophagy, lipid metabolism, and miRNA regulation, which are involved in the development of HCMV-associated atherogenesis. Gaining an improved understanding of these mechanisms will facilitate the development of novel and effective therapeutic strategies for the treatment of HCMV-related cardiovascular disease.

Long story short: p53 mediates innate immunity

The story of p53 and how we came to understand it is punctuated by fundamental insights into the essence of cancer. In the decades since its discovery, p53 has been shown to be centrally involved in most, if not all, of the cellular processes that maintain tissue homeostasis. Extensive functional analyses of p53 and its tumor-associated mutants have illuminated many of the common defects shared by most cancer cells. As the central character in a tale that continues to unfold, p53 has become increasingly familiar and yet remains surprisingly inscrutable. New relationships periodically come to light, and surprising, novel activities continue to emerge, thereby revealing new dimensions and aspects of its function. What lies at the very core of this complex protagonist? What is its prime motivation? As every avid reader knows, the elements of character are profoundly shaped by adversity--originating from within and without. And so it is with p53. This review will briefly recap the coordinated responses of p53 to viral infection, and outline a hypothetical model that would explain how an abundance of seemingly unrelated phenotypic attributes may in the end reflect a singular function. All stories eventually draw to a conclusion. This epic tale may eventually leave us with the realization that p53, most simply described, is a protein that evolved to mediate immune surveillance.

Innate nuclear sensor IFI16 translocates into the cytoplasm during the early stage of in vitro human cytomegalovirus infection and is entrapped in the egressing virions during the late stage

Intrinsic immune mechanisms mediated by constitutively expressed proteins termed "restriction factors" provide frontline antiviral defense. We recently demonstrated that the DNA sensor IFI16 restricts human cytomegalovirus (HCMV) replication by downregulating viral early and late but not immediate-early mRNAs and their protein expression. We show here that at an early time point during the in vitro infection of low-passage-number human embryonic lung fibroblasts, IFI16 binds to HCMV DNA. However, during a later phase following infection, IFI16 is mislocalized to the cytoplasmic virus assembly complex (AC), where it colocalizes with viral structural proteins. Indeed, upon its binding to pUL97, IFI16 undergoes phosphorylation and relocalizes to the cytoplasm of HCMV-infected cells. ESCRT (endosomal sorting complex required for transport) machinery regulates the translocation of IFI16 into the virus AC by sorting and trafficking IFI16 into multivesicular bodies (MVB), as demonstrated by the interaction of IFI16 with two MVB markers: Vps4 and TGN46. Finally, IFI16 becomes incorporated into the newly assembled virions as demonstrated by Western blotting of purified virions and electron microscopy. Together, these results suggest that HCMV has evolved mechanisms to mislocalize and hijack IFI16, trapping it within mature virions. However, the significance of this IFI16 trapping following nuclear mislocalization remains to be established.

IMPORTANCE

Intracellular viral DNA sensors and restriction factors are critical components of host defense, which alarm and sensitize immune system against intruding pathogens. We have recently demonstrated that the DNA sensor IFI16 restricts human cytomegalovirus (HCMV) replication by downregulating viral early and late but not immediate-early mRNAs and their protein expression. However, viruses are known to evolve numerous strategies to cope and counteract such restriction factors and neutralize the first line of host defense mechanisms. Our findings describe that during early stages of infection, IFI16 successfully recognizes HCMV DNA. However, in late stages HCMV mislocalizes IFI16 into the cytoplasmic viral assembly complex and finally entraps the protein into mature virions. We clarify here the mechanisms HCMV relies to overcome intracellular viral restriction, which provides new insights about the relevance of DNA sensors during HCMV infection.

Human cytomegalovirus pUL29/28 and pUL38 repression of p53-regulated p21CIP1 and caspase 1 promoters during infection

During infection by human cytomegalovirus (HCMV), the tumor suppressor protein p53, which promotes efficient viral gene expression, is stabilized. However, the expression of numerous p53-responsive cellular genes is not upregulated. The molecular mechanism used to manipulate the transcriptional activity of p53 during infection remains unclear. The HCMV proteins IE1, IE2, pUL44, and pUL84 likely contribute to the regulation of p53. In this study, we used a discovery-based approach to identify the protein targets of the HCMV protein pUL29/28 during infection. Previous studies have demonstrated that pUL29/28 regulates viral gene expression by interacting with the chromatin remodeling complex NuRD. Here, we observed that pUL29/28 also associates with p53, an additional deacetylase complex, and several HCMV proteins, including pUL38. We confirmed the interaction between p53 and pUL29/28 in both the presence and absence of infection. HCMV pUL29/28 with pUL38 altered the activity of the 53-regulatable p21CIP1 promoter. During infection, pUL29/28 and pUL38 contributed to the inhibition of p21CIP1 as well as caspase 1 expression. The expression of several other p53-regulating genes was not altered. Infection using a UL29-deficient virus resulted in increased p53 binding and histone H3 acetylation at the responsive promoters. Furthermore, expression of pUL29/28 and its interacting partner pUL38 contributed to an increase in the steady-state protein levels of p53. This study identified two additional HCMV proteins, pUL29/28 and pUL38, which participate in the complex regulation of p53 transcriptional activity during infection.

Equine arteritis virus induced cell death is associated with activation of the intrinsic apoptotic signalling pathway

Equine arteritis virus (EAV) causes a respiratory and reproductive disease in horses, equine viral arteritis. Though cell death in infection with EAV is considered to occur by apoptosis, the underlying molecular mechanism has not been extensively elucidated. We investigated the expression of mRNA of pro-apoptotic and caspase genes during EAV infection in BHK21 cells, a well-established cell type for EAV replication. Using a SYBR Green real-time PCR, mRNA of p53, Bax, caspase 3 and caspase 9 were found up-regulated in a time dependent manner in EAV infected cells. Western blot analysis for caspase 3 and caspase 9 showed expression of cleaved forms of these proteins during EAV infection. In addition, a luminescence-based cell assay for caspase 3/7 activation as a hallmark in apoptosis confirmed apoptotic cell death. The findings demonstrate that cell death in EAV infected BHK21 cells results from apoptosis mediated through the intrinsic signalling pathway.

PKCζ mediates disturbed flow-induced endothelial apoptosis via p53 SUMOylation

Disturbed flow-mediated PKCζ–PIASy association is critical for p53 SUMOylation and induces p53 nuclear export and endothelial cell apoptosis.

Atherosclerosis is readily observed in regions of blood vessels where disturbed blood flow (d-flow) is known to occur. A positive correlation between protein kinase C ζ (PKCζ) activation and d-flow has been reported, but the exact role of d-flow–mediated PKCζ activation in atherosclerosis remains unclear. We tested the hypothesis that PKCζ activation by d-flow induces endothelial cell (EC) apoptosis by regulating p53. We found that d-flow–mediated peroxynitrite (ONOO⁻) increased PKCζ activation, which subsequently induced p53 SUMOylation, p53–Bcl-2 binding, and EC apoptosis. Both d-flow and ONOO⁻ increased the association of PKCζ with protein inhibitor of activated STATy (PIASy) via the Siz/PIAS-RING domain (amino acids 301–410) of PIASy, and overexpression of this domain of PIASy disrupted the PKCζ–PIASy interaction and PKCζ-mediated p53 SUMOylation. En face confocal microscopy revealed increases in nonnuclear p53 expression, nitrotyrosine staining, and apoptosis in aortic EC located in d-flow areas in wild-type mice, but these effects were significantly decreased in p53^−/− mice. We propose a novel mechanism for p53 SUMOylation mediated by the PKCζ–PIASy interaction during d-flow–mediated EC apoptosis, which has potential relevance to early events of atherosclerosis.

Interference with p53 functions in human viral infections, a target for novel antiviral strategies?

Viral infections cause a major stress in host cells. The cellular responses to stress are mediated by p53, which by deregulation of cell cycle and apoptosis, may also be part of the host cell reaction to fight infections. Therefore, during evolutionary viral adaptation to host organisms, viruses have developed strategies to manipulate host cell p53 dependent pathways to facilitate their viral life cycles. Thus, interference with p53 function is an important component in viral pathogenesis. Many viruses have proteins that directly affect p53, whereas others alter the regulation of p53 in an indirect manner, mediated by Hdm2 or Akt, or induction of interferon. Rescue of p53 activity is becoming an area of therapeutic development in oncology. It might be feasible that manipulation of p53 mediated responses can become a therapeutic option to limit viral replication or dissemination. In this report, the mechanisms by which viral proteins manipulate p53 responses are reviewed, and it is proposed that a pharmacological rescue of p53 functions might help to control viral infections.

Assessment of peripheral endothelial-dependent vasodilatation within the first year after heart transplantation

BACKGROUND

Peripheral endothelial dysfunction (ED) has been found in patients with severe heart failure. Whether ED improves after heart transplantation (HTx) is still a matter of controversy.

METHODS

Forearm endothelium-dependent vasoreactivity was assessed in 40 patients after HTx. Flow-mediated vasodilatation (FMD) was measured by high-resolution brachial artery ultrasound to assess endothelial function at 1, 6, and 12 months after HTx. Cardiac allograft vasculopathy (CAV) was assessed by coronary angiography at 1 and 12 months and by intravascular ultrasound (IVUS) at 1 year.

RESULTS

Mean FMD at 1 month was 1.9% +/- 2.6%, improving to 3.3% +/- 3.2% at 6 months (p < 0.005) and to 5.1% +/- 3.4% at 1 year (p < 0.0001). FMD was significantly impaired in 33 patients (82%) at 1 month, in 27 (67%) at 6 months, and in 19 (47%) at 1 year after HTx. CAV was diagnosed by IVUS in 19 patients (63%) at 1 year. Patients without peripheral ED at 1 month had lower incidence of increased intimal thickness of 0.5 mm or more at 1 year after HTx (20% vs 75%, p < 0.01).

CONCLUSIONS

Impairment of peripheral FMD was highly prevalent soon after HTx and was present in nearly 50% of patients at 1 year. Patients without peripheral ED at 1 month were associated with lower probability of CAV. Although more studies are needed, the evaluation of peripheral endothelial function at 1 month after HTx could be potentially useful to identify patients at lower risk of CAV.

Impaired p53 binding to importin: a novel mechanism of cytoplasmic sequestration identified in oxaliplatin-resistant cells

Previous studies have described one nuclear localization signal (NLSI) in p53 and speculated on two additional sites termed NLSII and NLSIII. Drug-resistant KB cells selected with cisplatin or oxaliplatin were found to have increased p53 levels and in oxaliplatin-selected cells, a larger p53 predominantly in the cytoplasm. In oxaliplatin-selected cells a single nucleotide deletion in the sequence-encoding amino acid 382, part of NLSIII, resulted in a frame shift and a 420 amino acid protein (p53(420)). We investigated explanations for the cytoplasmic sequestration of p53(420) while assessing the role, if any, of NLSII and NLSIII in p53 nuclear import. We found that neither NLSII nor NLSIII are essential for p53 nuclear localization. Furthermore, we confirmed p53(420) is able to tetramerize, transactivate a p21 promoter, bind dynein and that the reduced nuclear accumulation is not a consequence of increased p53 nuclear export. However, the association of p53(420) with importin-beta, essential for nuclear import, was significantly impaired. We conclude that despite sequence similarity to consensus NLSs neither NLSII nor NLSIII have roles in p53 nuclear transport. We also identified impaired association with importin as a novel mechanism of p53 cytoplasmic sequestration that impairs nuclear transport rendering cells functionally deficient in p53.

TGF-beta and IL-6 signals modulate chromatin binding and promoter occupancy by acetylated FOXP3

Expression of FOXP3, a potent gene-specific transcriptional repressor, in regulatory T cells is required to suppress autoreactive and alloreactive effector T cell function. Recent studies have shown that FOXP3 is an acetylated protein in a large nuclear complex and FOXP3 actively represses transcription by recruiting enzymatic corepressors, including histone modification enzymes. The mechanism by which extracellular stimuli regulate the FOXP3 complex ensemble is currently unknown. Although TGF-beta is known to induce murine FOXP3(+) Treg cells, TGF-beta in combination with IL-6 attenuates the induction of FOXP3 functional activities. Here we show that TCR stimuli and TGF-beta signals modulate the disposition of FOXP3 into different subnuclear compartments, leading to enhanced chromatin binding in human CD4(+)CD25(+) regulatory T cells. TGF-beta treatment increases the level of acetylated FOXP3 on chromatin and site-specific recruitment of FOXP3 on the human IL-2 promoter. However, the proinflammatory cytokine IL-6 down-regulates FOXP3 binding to chromatin in the presence of TGF-beta. Moreover, histone deacetylation inhibitor (HDACi) treatment abrogates the down-regulating effects of IL-6 and TGF-beta. These studies indicate that HDACi can enhance regulatory T cell function via promoting FOXP3 binding to chromatin even in a proinflammatory cellular microenvironment. Collectively, our data provide a framework of how different signals affect intranuclear redistribution, posttranslational modifications, and chromatin binding patterns of FOXP3.